FLAT CREEK WATERSHED IMPROVEMENT DISTRICT

May 5, 2017.  Teton County Emergency Management held a flood meeting to prepare for a potential flood season.  Please visit the link below to download the slide presentation, Teton/Jackson Flood Pre-Plan, levee map, and the "Ready Set Go" brochure.

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 Flat Creek Water Improvement District

Emergency Wintertime and Spring Runoff Action Plan

Effective Date: March 11, 2019

 

Background:

Although spring run-off flooding has occurred along Flat Creek, it is uncommon and of secondary concern of the Flat Creek Water Improvement District (WID). However, winter flooding of Flat Creek is a natural and common occurrence. It happens during extended periods of sub-zero weather. Though the process is complex and not completely understood, what is known is this: water molecules get flung into the super-cold air through wave action (or through other atmospheric phenomena), freeze and fall back into the stream where they may congeal into visible globs known as frazil ice. Water currents then carry the frazil ice to the stream’s bed where it freezes to the substrate forming anchor ice. This process can continue as long as open water is exposed to super-cold air.

 

As the anchor ice “grows” from the bottom up, it lifts the flowing water until it spills over the shelf ice forming from the banks. And as long as sub-zero temperatures continue and shelf ice doesn’t close off the flowing water, the stream can continue to rise until it eventually over spills the banks, threatening private property. In addition, extended periods of anchor ice buildup commonly lead to the formation of ice dams that greatly increase the flooding threat.

 

In the past, the Town of Jackson (“TOJ”) has addressed the issue in two ways: First, it installed 3 thaw wells that draw warm ground water up and pour it into the creek, thus warming the flowing water. Preliminary data suggests that this practice may help alleviate icing for 200 to 400 yards downstream before the new water chills to ambient stream temperature. Unless thaw wells can be placed at the properly spaced locations, their usefulness is very limited- plus they are costly to install and operate.

 

Second, when floodwaters threatened private structures, the TOJ’s response has been to order backhoes into the creek to break up and remove the ice. This too is expensive and has obvious detrimental impacts on the streambed and shoreline where the ice blocks are dumped. Though this eliminates the immediate threat of flood damage, it is not a long-term solution.

 

The WID was formed late in 2014 to address this winter flooding issue, and as a first order of business, it has taken over the responsibility of responding to the immediate threats of winter flooding. To this end, the WID is working in partnership with the TOJ and the Teton Conservation District.

 

The WID has developed the following strategies to (1) respond to the imminent threat of winter flooding and (2) identify and apply a long-term preventative solution(s) to the winter (and spring time) flooding of Flat Creek that poses an imminent threat to private structures:

 

WID Emergency Wintertime Action Plan

 

The WID Board Action Plan:

• To receive signed copies of the “Right-of-Entry/Release/Hold Harmless Agreement” forms from WID members for year-around monitoring, data collection, conducting watershed improvements, and responding to flooding threats within the WID boundaries.

 

• Monitor the creek flows and icing levels on a daily basis by a team of trained volunteers and when necessary, by paid staff. Key areas to monitor are:

       Berger Lane

       The Stellaria Lane Bridge

       Shelby Lane area

       Garaman Park Bridge

       Area South of the new post office

       Dogwood Drive cul-de-sac area

       Stacey Lane cul-de-sac area

       Willow Park Bridge south of Virginian Lane

 

• Monitor weather predictions on a daily basis. If weather projections indicate a long period of sub-zero temperature it may be affective to turn the thaw wells on. Monitor the effects created from the thaw well water flows on a daily basis. Procedure for activating thaw wells: Contact appropriate TOJ personnel in accordance with WID/TOJ Memorandum of Understanding dated 12/21/15. TOJ responsible for obtaining any and all permits necessary to operate thaw wells.

 

• Determine when and where to bring mechanical equipment into the WID portion of the creek to prevent flood damage to private structures. This decision shall be made by the WID Board of Directors in consultation with TOJ personnel. The determination shall consider at minimum the following criteria: current and predicted weather patterns, speed at which flood waters and ice buildup are occurring, and proximity of flood waters to private structures with an understanding of the time required to place equipment into the creek.

 

• Many areas of the pathway near Garaman Park get flooded every year. This is due to the fact that they were constructed within the normal flood levels. Action should not be taken solely to clear pathway flooding.

 

• Prior to placing any equipment in the creek a FEMA Flood Plain permit must be obtained by the TOJ.

 

• Sand bags and sand should be made available to the public through the winter months. TOJ has these on hand and will have sand available at Town maintenance shop.

 

• Be prepared to communicate with WID residents via e-mail blasts, PSA’s, and set up NixLe system with Teton County Emergency Management to advise the public of possible flooding/icing events.

 

Action Plan for TOJ’s Thaw Wells:

 

• The use of the thaw wells must be coordinated with the TOJ as described in Exhibit A of the December 21st, 2015 Memorandum of UnderstandingBetween the Town of Jackson and the Flat Creek Water Improvement District and attached herein.

 

Sub-contracting of Excavators Action Plan:

 

• Prepare a list of qualified excavation sub-contractors with all pertinent contact information: e.g. company name, list of excavators with sizes and quantities, to be ready on a monuments notice to enter Flat Creek within the WID boundaries anytime between mid-November and end of February.

 

• The use of mechanical methods to removing ice should always start at the downstream areas of the creek and slowly progress upstream in order to realize a higher probability of reducing water levels within the creek system. In addition, clearing the lower sections of ice first, allows a better chance that ice escaping from upstream work will not clog down stream flows.

 

• When multiple equipment is being used to remove ice from the creek, it is recommended that the upstream equipment be supported by a downstream equipment which can “catch and remove” ice which escaped from the upstream equipment. By using this method the chance of forming new ice jams downstream is greatly        . reduced.

 

FCWID Long-term Action Plan to Prevent Flood Damage to Private Structures

 

The long-term goal of the WID is to identify and apply procedures that will prevent damage to private structures due to winter (and spring) flooding of Flat Creek within the WID boundaries. Any actions taken will be evaluated in regards to their impacts upon the year-around aquatic and riparian habitat quality and function, and whenever appropriate and possible, will attempt to mitigate previous man-caused disturbances and improve upon the overall ecological function and value of the Flat Creek corridor.

 

Unfortunately, there is very little information identifying proven actions that might eliminate frazil ice-caused winter flooding on small streams such as Flat Creek. Consequently, the WID’s immediate goal is to engage qualified consultants to collect and analyze a range of winter atmospheric and stream data in an attempt to identify the environmental circumstances that lead to major flooding episodes. (The first year of data collection extended from mid-November, 2015 to mid-February, 2016.) Once we have a better understanding of the full range of circumstances leading to flooding, the work of identifying and applying solutions will begin.

 

It is likely that as the first season’s data is analyzed, information gaps will appear. It is also anticipated that with data analysis, patterns will begin to present themselves that may require the collection of additional or different data. This will likely require the WID to adjust efforts and continue collecting data for several more years.

 

Long-term actions that might be taken to prevent property damage from winter flooding include, but are not limited to: installation of additional thaw wells, placement of structures within the stream that alter the hydrology so as to eliminate the formation of frazil ice, construction of berms in select locations, and the closing of abandoned irrigation ditches (which, in flood situations can direct flood water out of the stream and onto private property). These and other as yet unidentified actions may be used exclusively, but more likely in combination depending on conditions and locations. The construction of berms in select locations and the closure of abandoned irrigation ditches may begin as soon as these locations are identified and appropriate permits obtained.

 

All flood prevention actions will be undertaken in coordination with the Teton Conservation District, The Town of Jackson, The Army Corps of Engineers and the Federal Emergency Management Agency, and with consultation with the Wyoming Game and Fish Department.

 

EXHIBIT A

 

It should be noted that when using Town Thaw Wells, it is best to turn the wells on from the most southern area (Thaw Well #3) and monitor the effects on the entire stream before powering up upstream well #2.

 

The use of the Thaw wells should be coordinated with the Town. Each time a Thaw Well is turned on and off the Town must completed sampling of the water and report flow volumes and send the data to the DEQ. As such it is not a good practice to continually turn the wells on and off.

 

It should be noted that when using Thaw wells it is best to turn the wells on from the most southern area (thaw Well #3) monitor the effects on the entire stream before powering up the upstream wells #1, and #2.

 

       Thaw Well #1 is in Karns Meadow:

• Well #1 can provided approximately 1,400 GPM. We have found that the thawing created from this will does not affect the icing backup at the Virginian Lane Bridge. So it’s effectiveness to clear icing is minimal. In addition the use of this well actually opens up a channel in the creek that allows additional floodwater to drain thru the system, which could create additional flooding. It is best to allow the ice to remain in Karns Meadow so icing and water can be stored in that area without effecting building and private property.

 

• Should this well be turn on the Town would need to turn the potable water well off and reconfigure all of the water systems PRV (pressure reducing vaults) to supply drinking water to central area of Town.

 

• The use of this thaw well is not recommended, if at all possible.

 

       Thaw Well #2 is located in the park south of Powderhorn Lane: 

• Well #2 can produce approximately 900 GPM and depending on weather conditions could help reduce icing effects between Powderhorn Lane and Stellaria Lane. This well discharge just above the pathway bridge within the park, as such the use of this well can clear icing lodged on the upstream area of the creek.

 

       Thaw Well #3 is located next to the High School Road Bridge: 

• Well #3 can produce approximately 400 GPM and when used creates minimal effects of the upstream icing of the creek. In addition this well has an oscillating ground water supply and often shorts out due to cavitation.